1. Field of the Invention
This invention relates to a process for the production of open-cell foams containing urethane groups which may be highly elastic and to the foams produced by this process.
2. Description of the Prior Art
Soft, elastic polyurethane foams are widely used in the upholstery industry for the manufacture of upholstered seats and seat backs. Soft, elastic foams are expected to be as comfortable to sit on as foams of natural latex or a combination of standard upholstery materials such as feathers, natural hair or wadding.
A foam intended for use in the upholstery industry is also expected to show maximum strength properties to avoid splitting under mechanical loads of the type applied, for example, during covering with textiles, coupled with extreme hardness for a given gross density (kg/m.sup.3). For economic reasons, particular preference is attributed to foams having gross densities of from 15 to 40 kg/m.sup.3.
In order to meet these various requirements, attempts have been made to use inert organic or inorganic fillers. In this connection, it is known that solid additives may be introduced into one of the components used for foaming or directly into the foaming mixture, for example by directly introducing the fillers into the mixing chamber of a foaming machine. Attempts have also been made to carry out polymerization reactions in the polyols used for foaming. For example, dispersions of copolymers of styrene and acrylonitrile in polyethers containing hydroxyl groups are well known and commercially available.
In conventional foaming processes, tertiary amines are generally used as catalysts. In addition to an unpleasant odor, catalysts such as these have the disadvantage that they attack the lacquer finishes of upholstered furniture. In particular, the nitrocellulose lacquers frequently used are destroyed by the tertiary amines. In addition, it has not yet been possible on an industrial scale to foam mixtures of TDI (tolylene diisocyanate) and MDI (4,4'- and/or 2,4'-diphenylmethane diisocyanate) in soft foam block formulations in such a way that foams having increased indentation hardness are obtained (cf. Comparison Example III).
The object of the present invention is to avoid these disadvantages and, in addition, to provide in a technically simple manner foams which can be produced in a very wide range of gross densities and which show extreme hardness for a predetermined gross density.
Surprisingly, this object can be achieved by carrying out production of the polyurethane foams from polyols, polyisocyanates, water, and, optionally, emulsifiers, stabilizers and organic blowing agents in the presence of the combination according to the invention of catalysts, a compound containing labile halogen and, optionally, crosslinking agents. The fact that this particular combination (when crosslinking agents are present) gives highly elastic foams having the higher hardness levels required is surprising and was not foreseeable to the skilled artisan because it was known from the chemistry of rigid foams that this form of catalysis leads to isocyanurate structures and that the additional use of crosslinking agents generally leads to brittle polyurethane plastics. Accordingly, it may be regarded as extremely surprising that the catalysts according to the invention accelerate urethane and urea formation because the very catalysts described as suitable are known as polymerization catalysts for isocyanates. Through the process according to the invention, it has been possible to produce foams which, despite their extreme hardness, resemble latex foam in character and can be produced without any odor whatever, depending on the application envisaged.
According to the invention, the combination of crosslinking agent, catalyst and a substance containing labile halogen is preferred because, otherwise, either the foam reaction mixture would collapse (Comparison Example I), or foams disintegrating after aging in hot air would be obtained (Comparison Example II). If the process of the invention is carried out without the specific crosslinking agent, "super-soft" foams are obtained. The preparation of these foams is also an object of the present invention.